Biomass materials such as corn stover, wheat straw, alfalfa, grasses, rice straw, corn fiber, distiller's dried grains with solids, switchgrass, bagasse, and the like contain cellulosic material and proteins that may be used in fermentation processes, as animal feeds, or for other purposes. However, the availability of these materials is low in untreated biomass material. Various processes and pretreatments of biomass material have been used to increase the availability of useful materials in biomass. These processes include dry milling, wet milling, steam explosion, and chemical pretreatment such as the ammonia fiber explosion (AFEX) process.
These processes have several drawbacks. Dry milling is less effective for increasing the availability of the cellulosic materials and proteins in biomass material than other techniques. Wet milling, while more effective than dry milling, incurs greater energy costs which limits the economic feasibility of the process. Also, continuous steam explosion processes are energy intensive and require additional separation steps to recover volatile organics that are stripped from the biomass by the steam. The AFEX process, however, is a unique chemical pretreatment.
Up to now, the AFEX process has been primarily carried out as a batch process, which limits the ability to commercially apply the process. In the AFEX process, the biomass material is typically contacted with liquid ammonia at an elevated pressure for a sufficiently long time for the ammonia to swell the biomass material. After the biomass fibers have been swollen with liquid ammonia, the pressure may be rapidly decreased to a level below the vapor pressure of the ammonia such that the ammonia vaporizes and ruptures the biomass fibers. This makes more of the cellulosic material and proteins available for down stream processes or for animal feed.
Attempts to create a continuous AFEX process have shown that the swelling process may be carried out in extrusion reactors. However, these attempts have not effectively provided for the efficient recovery and recycle of the ammonia used to swell the biomass fibers. According to some designs, the ruptured biomass is dried and the vapor containing swelling agent and water is condensed and distilled so that purified swelling agent may be recycled to the reactor. This distillation process is expensive, both in capital expense, and in energy costs.
Accordingly, there is a need for a continuous AFEX process that is more commercially feasible than prior designs. Further, there is a need for a continuous AFEX process that provides for the effective recovery and purification of vaporized ammonia. Further still, there is a need for a continuous AFEX process that provides for efficient recovery of the portion of ammonia that remains with the biomass after the rapid depressurization.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The present application is directed to those processes and embodiments disclosed herein, regardless of whether they accomplish one or more of the aforementioned needs.